In recent years, it has become common practice that a camera is incorporated in a personal computer or game console for capturing images of a user for use in a variety of forms. For example, some technologies that are commercially available today such as TV phone and video chat are designed to transmit user's images to other end in an as-is manner via a network. Other technologies recognize user's motions by image analysis and use such motions as input information for games and information processing (refer, for example, to PTL 1 and NPL 1). Further, it has become possible in recent years to provide a game which is better sense of realism and image representation by detecting object's motions in a three-dimensional space including the depth direction with high accuracy.